Cerebral Cortex Membranes Research Articles

High-Fat and Resveratrol Supplemented Diets Modulate Adenosine Receptors in the Cerebral Cortex of C57BL/6J and SAMP8 Mice.

Neurodegenerative disorders are devastating diseases in which aging is a major risk factor. High-fat diet (HFD) seems to contribute to cognition deterioration, but the underlying mechanisms are poorly understood. Moreover, resveratrol (RSV) has been reported to counteract the loss of cognition associated with age. Our study aimed to investigate whether the adenosinergic system and plasma membrane cholesterol are modulated by HFD and RSV in the cerebral cortex of C57BL/6J and SAMP8 mice. Results show that HFD induced increased A1R and A2AR densities in C57BL/6J, whereas this remained unchanged in SAMP8. Higher activity of 5′-Nucleotidase was found as a common effect induced by HFD in both mice strains. Furthermore, the effect of HFD and RSV on A2BR density was different depending on the mouse strain. RSV did not clearly counteract the HFD-induced effects on the adenosinergic system. Besides, no changes in free-cholesterol levels were detected in the plasma membrane of cerebral cortex in both strains. Taken together, our data suggest a different modulation of adenosine receptors depending on the mouse strain, not related to changes in plasma membrane cholesterol content.

Changes in [3H]-ouabain and [3H]-neurotensin binding to rat cerebral cortex membranes after administration of antipsychotic drugs haloperidol and clozapine

Evidences indicate the relationship between neurotensinergic and dopaminergic systems. Neurotensin inhibits synaptosomal membrane Na+, K+-ATPase activity, an effect blocked by SR 48692, antagonist for high affinity neurotensin receptor (NTS1) type. Assays of high affinity [3H]-ouabain binding (to analyze K+ site of Na+, K+-ATPase) show that in vitro addition of neurotensin decreases binding. Herein potential interaction between NTS1 receptor, dopaminergic D2 receptor and Na+, K+-ATPase was studied. To test the involvement of dopaminergic D2 receptors in [3H]-ouabain binding inhibition by neurotensin, Wistar rats were administered i.p.with antipsychotic drugs haloperidol (2mg/kg) and clozapine (3, 10 and 30mg/kg). Animals were sacrificed 18h later, cerebral cortices harvested, membrane fractions prepared and high affinity [3H]-ouabain binding assayed in the absence or presence of neurotensin at a 10 micromolar concentration. No differences versus controls for basal binding or for binding inhibition by neurotensin were recorded, except after 10mg/kg clozapine. Rats were administered with neurotensin (3, 10y 30μg, i.c.v.) and 60min later, animals were sacrificed, cerebral cortices harvested and processed to obtain membrane fractions for high affinity [3H]-ouabain binding assays. Results showed a slight but statistically significant decrease in binding with the 30μg neurotensin dose. To analyze the interaction between dopaminergic D2 and NTS1 receptors, [3H]-neurotensin binding to cortical membranes from rats injected with haloperidol (2mg/kg, i.p.) or clozapine (10mg/kg) was assayed. Saturation curves and Scatchard transformation showed that the only statistically significant change occurred in Bmax after haloperidol administration. Hill number was close to the unit in all cases. Results indicated that typical and atypical antipsychotic drugs differentially modulate the interaction between neurotensin and Na+, K+-ATPase. At the same time, support the notion of an interaction among dopaminergic and neurotensinergic systems and Na+, K+-ATPase at central synapses.

The Administration of Levocabastine, a NTS2 Receptor Antagonist, Modifies Na+, K+-ATPase Properties

Neurotensin behaves as a neuromodulator or as a neurotransmitter interacting with NTS1 and NTS2 receptors. Neurotensin in vitro inhibits synaptosomal membrane Na(+), K(+)-ATPase activity. This effect is prevented by administration of SR 48692 (antagonist for NTS1 receptor). The administration of levocabastine (antagonist for NTS2 receptor) does not prevent Na(+), K(+)-ATPase inhibition by neurotensin when the enzyme is assayed with ATP as substrate. Herein levocabastine effect on Na(+), K(+)-ATPase K(+) site was explored. For this purpose, levocabastine was administered to rats and K(+)-p-nitrophenylphosphatase (K(+)-p-NPPase) activity in synaptosomal membranes and [(3)H]-ouabain binding to cerebral cortex membranes were assayed in the absence (basal) and in the presence of neurotensin. Male Wistar rats were administered with levocabastine (50μg/kg, i.p., 30min) or the vehicle (saline solution). Synaptosomal membranes were obtained from cerebral cortex by differential and gradient centrifugation. The activity of K(+)-p-NPPase was determined in media laking or containing ATP plus NaCl. In such phosphorylating condition enzyme behaviour resembles that observed when ATP hydrolyses is recorded. In the absence of ATP plus NaCl, K(+)-p-NPPase activity was similar for levocabastine or vehicle injected (roughly 11μmole hydrolyzed substrate per mg protein per hour). Such value remained unaltered by the presence of 3.5×10(-6)M neurotensin. In the phosphorylating medium, neurotensin decreased (32%) the enzyme activity in membranes obtained from rats injected with the vehicle but failed to alter those obtained from rats injected with levocabastine. Levocabastine administration enhanced (50%) basal [(3)H]-ouabain binding to cerebral cortex membranes but failed to modify neurotensin inhibitory effect on this ligand binding. It is concluded that NTS2 receptor blockade modifies the properties of neuronal Na(+), K(+)-ATPase and that neurotensin effect on Na(+), K(+)-ATPase involves NTS1 receptor and -at least partially- NTS2 receptor.

Allosteric effect of serotonin and mianserin on the kinetics of specific [3H]-ligand binding to adrenergic and muscarinic receptors in the rat cerebral cortex membranes

The effects of serotonin receptor activation (by serotonin) and inhibition (by mianserin) on the properties of the α1-, α2-adrenoreceptors, and muscarinic cholinergic receptors in subcellular membrane fractions from the rat cerebral cortex were studied. Experimental data on the kinetics of specific antagonists binding to adrenergic and muscarinic receptors were analyzed by graphical and mathematical methods. The results suggest the presence of allosteric (cross-talk) interaction. In the control, α1- and α2-adrenoreceptors were represented by a single pool, and muscarinic receptors, by two pools. Two pools of adrenoreceptors with different affinity were detected against the background of serotonin. It was found that mianserin induces the formation of two pools of only (α2-receptors and muscarinic receptors are represented by two pools differing in the main parameters, such as dissociation constants and adrenoreceptor concentrations, in the control and experimental groups. It was shown that the allosteric effect of serotonin and mianserin is manifested in the inhibition of muscarinic receptors. It was assumed that the adrenergic and cholinergic receptors exist as dimers. The interaction between the adrenergic, cholinergic, and serotonergic systems is likely to be implemented at the cell membrane level.

Serotoninergic agonist and antagonist are modulators of the α2-adrenoceptor activity in rat brain cortex membranes

The influence of activation and inhibition of serotonin receptors by serotonin (5HT) and miancerin on binding of specific nonselective α2-antagonist [3H]RX821002 in rat cerebral cortex membranes was studied. It was shown that the ligand-receptor interaction for α2-adrenoceptors corresponded to the model suggesting the presence of one pool of receptors and binding of two ligand molecules to the receptor. The parameters of the [3H]RX821002 binding to α2-adrenoceptors were as follows: Kd = 1.57 ± 0.276 nM, Bmax = 7.24 ± 1.63 fmol/mg protein, n = 2. In the case of activation of 5HT-receptors by serotonin, the character of ligand binding was different: two pools of receptors were detected with the parameters Kd1 = 0.82 ± 0.06; Kd2 = 2.65 ± 0.22 nM; Bm1 = 1.65 ± 0.23; Bm2 = 4.20 ± 0.11 fmol/mg protein; n = 2. The affinity of high-affinity receptors increased twofold and the affininty of low-affinity receptors decreased by 69% as compared to control values. The concentration of high-affinity receptors decreased 4.4-fold, and of low-affinity, 1.7-fold. The value of maximal reaction (Bmax) decreased by 20%. In the case of miancerin-induced inhibition of 5HT-receptors the character of ligand binding also changed; two pools of receptors were detected with the following parameters: Kd1 = 0.48 ± 0.09; Kd2 = 3.79 ± 0.71 nM; B1 = 0.63 ± 0.17; B2 = 4.75 ± 0.21 fmol/mg protein; n = 2. The affinity of high-affinity receptors pool increased by 70% and that of low-affinity receptors decreased by 76% as compared to control values. The concentration of active high-affinity and low-affinity α2-adrenoceptors decreased by 70% and 141%, respectively. The total amount of the receptors (Bmax) decreased by 26%. The data suggest that α2-adrenoceptors in rat cerebral cortex exist as dimers. Modulatory effects of serotonin and miancerin on specific antagonist binding to α2-adrenoceptors may be accomplished by altering the character and binding parameters of the nonselective α2-antagonist [3H]RX821002.

Serotoninergic agonists and antagonists are the modulators of α1-Adrenoceptor activity in rat brain cortical membranes

The effects of activation and inhibition of serotonin receptors by serotonin (5-HT) and mianserin on the specific nonselective α1-antagonist [3H]prazosine binding in rat cerebral cortex membranes was studied. It was shown that the ligand-receptor interaction of α1-adrenoceptors corresponded to the model suggesting the presence of one pool of receptors and the binding of two ligand molecules to the receptor. The parameters of [3H]prazosine binding to α1-adrenoceptors were as follows: Kd =1.85 ± 0.16 nM, Bmax = 31.1 ± 0.3 fmol/mg protein, n = 2. In case of activation of 5HT-receptors by serotonin, the character of ligand binding was different: two pools of receptors were detected with the parameters Kd1 = 0.61 ± 0.04, Kd2 = 3.82 ± 0.15 nM, Bm1 = 6.6 ± 0.7, Bm2 = 25.6 ± 0.4 fmol/mg protein, n = 2. The sensitivity of the high-affinity pool increased threefold and the sensitivity of the low-affinity pool decreased twofold as compared to the control. The value of maximal reaction (Bmax) did not change. In the case of inhibition of 5HT-receptors by mianserin, radioactive ligand is bound to α1-adrenoceptors according to the same model as in the control conditions. The affinity of α1-adrenoceptors to [3H]prazosine decreases twofold and the concentration increases (Kd = 3.97 ± 0.12 nM, Bmax = 40.0 ± 0.5 fmol/mg protein). The data suggest that α1-adrenoceptors in rat cerebral cortex exist as a dimer. The modulatory effects of serotonin and mianserin on the specific binding of [3H]prazosine to α1-adrenoceptors was detected, manifesting itself as changes in the binding parameters and in the general character of ligand-receptor interactions.

The histamine autoreceptor is a short isoform of the H3 receptor

BACKGROUND AND PURPOSE The histamine H(3) receptor was identified as the autoreceptor of brain histaminergic neurons. After its cloning, functional H(3) receptor isoforms generated by a deletion in the third intracellular loop were found in the brain. Here, we determined if this autoreceptor was the long or the short isoform. EXPERIMENTAL APPROACH We hypothesized that the deletion would affect H(3) receptor stereoselectivity. The effects of the enantiomers of two chiral ligands, N(α)-methyl-α-chloromethylhistamine (N(α) Me-αClMeHA) and sopromidine, were investigated on cAMP formation at the H(3(445)) and H(3(413)) receptor isoforms, common to all species. They were further compared with their effects at autoreceptors. They were also compared on [(35)S]GTPγ[S] binding to membranes of rat cerebral cortex, striatum and hypothalamus, the richest area in autoreceptors. KEY RESULTS The stereoselectivity of N(α) Me-αClMeHA enantiomers as agonists was similar at the H(3(413)) receptor isoform and autoreceptors, but lower at the long isoform. While (S) sopromidine did not discriminate between the isoforms, (R) sopromidine was an antagonist at the H(3(413)) receptor isoform and autoreceptors, but a full agonist at the long isoform. In rat brain, stereoselectivity of N(α) Me-αClMeHA was higher in the hypothalamus than in cerebral cortex or striatum, whereas the opposite pattern was found for sopromidine. CONCLUSIONS AND IMPLICATIONS The pharmacological profiles of H(3) receptor isoforms differed markedly, showing that the function of autoreceptors was fulfilled by a short isoform, such as the H(3(413)) receptor. Development of drugs selectively targeting autoreceptors might enhance their therapeutic efficacy and/or decrease incidence of side effects.

Hypnotic effects and GABAergic mechanism of licorice (Glycyrrhiza glabra) ethanol extract and its major flavonoid constituent glabrol

Licorice (Glycyrrhiza glabra, GG) is one of the most frequently used herbal medicines worldwide, and its various biological activities have been widely studied. GG is reported to have neurological properties such as antidepressant, anxiolytic, and anticonvulsant effects. However, its hypnotic effects and the mechanism of GG and its active compounds have not yet been demonstrated. In this study, GG ethanol extract (GGE) dose-dependently potentiated pentobarbital-induced sleep and increased the amount of non-rapid eye movement sleep in mice without decreasing delta activity. The hypnotic effect of GGE was completely inhibited by flumazenil, which is a well-known γ-aminobutyric acid type A-benzodiazepine (GABAA-BZD) receptor antagonist, similar to other GABAA-BZD receptor agonists (e.g., diazepam and zolpidem). The major flavonoid glabrol was isolated from the flavonoid-rich fraction of GGE; it inhibited [3H] flumazenil binding to the GABAA-BZD receptors in rat cerebral cortex membrane with a binding affinity (Ki) of 1.63μM. The molecular structure and pharmacophore model of glabrol and liquiritigenin indicate that the isoprenyl groups of glabrol may play a key role in binding to GABAA-BZD receptors. Glabrol increased sleep duration and decreased sleep latency in a dose-dependent manner (5, 10, 25, and 50mg/kg); its hypnotic effect was also blocked by flumazenil. The results imply that GGE and its flavonoid glabrol induce sleep via a positive allosteric modulation of GABAA-BZD receptors.

Neurotensin decreases high affinity [3H]-ouabain binding to cerebral cortex membranes

Previous work from this laboratory showed the ability of neurotensin to inhibit synaptosomal membrane Na+, K+-ATPase activity, the effect being blocked by SR 48692, a non-peptidic antagonist for high affinity neurotensin receptor (NTS1) [López Ordieres and Rodríguez de Lores Arnaiz 2000; 2001]. To further study neurotensin interaction with Na+, K+-ATPase, peptide effect on high affinity [3H]-ouabain binding was studied in cerebral cortex membranes. It was observed that neurotensin modified binding in a dose-dependent manner, leading to 80% decrease with 1×10−4M concentration. On the other hand, the single addition of 1×10−6M, 1×10−5M and 1×10−4M SR 48692 (Sanofi-Aventis, U.S., Inc.) decreased [3H]-ouabain binding (in %) to 87±16; 74±16 and 34±17, respectively. Simultaneous addition of neurotensin and SR 48692 led to additive or synergic effects. Partial NTS2 agonist levocabastine inhibited [3H]-ouabain binding likewise. Saturation assays followed by Scatchard analyses showed that neurotensin increased Kd value whereas failed to modify Bmax value, indicating a competitive type interaction of the peptide at Na+, K+-ATPase ouabain site. At variance, SR 48692 decreased Bmax value whereas it did not modify Kd value. [3H]-ouabain binding was also studied in cerebral cortex membranes obtained from rats injected i. p. 30min earlier with 100μg and 250μg/kg SR 48692. It was observed that the 250μg/kg SR 48692 dose led to 19% decrease in basal [3H]-ouabain binding. After SR 48692 treatments, addition of 1×10−6M led to additive or synergic effect. Results suggested that [3H]-ouabain binding inhibition by neurotensin hardly involves NTS1 receptor.

Pharmacological characterisation of the GlyT-1 glycine transporter using two novel radioligands

Inhibitors of the glycine transporter GlyT-1 are being developed as potential treatments for schizophrenia. Here we report on the use of two novel radioligands, [ 3H]-SB-733993 and [ 3H]-GSK931145, for the characterisation of GlyT-1 in both cells and native tissue. Binding was evaluated in membranes either from HEK293 cells expressing recombinant human GlyT-1 (hGlyT-1) or from rat cerebral cortex. Specific binding of both [ 3H]-SB-733993 and [ 3H]-GSK931145 to hGlyT-1 HEK293 cell membranes and rat cerebral cortex membranes was saturable and comprised >90% of total binding. K d and B max values for the two radioligands were fairly similar, with K d values of 1–2 nM and B max values of around 7000 fmol/mg protein in hGlyT-1 membranes and 3000 fmol/mg protein in rat cortex membranes. Association of [ 3H]-SB-733993 was faster, with binding reaching equilibrium within 30 min compared with 90 min for [ 3H]-GSK931145. Dissociation was also much slower for [ 3H]-GSK931145 than for [ 3H]-SB-733993, with 50% of specific binding being dissociated by approximately 40 min and 5 min, respectively. Autoradiography studies with [ 3H]-GSK931145 showed widespread distribution of binding in rat brain, with generally higher binding in caudal compared with rostral areas. Initial studies in human frontal cortex membranes showed clear specific binding of [ 3H]-GSK931145, though with much lower density ( B max 570 fmol/mg protein) and slightly lower affinity (K d 4.5 nM) compared with rat cortex. A human brain autoradiography study showed higher specific binding in cerebellum compared with frontal cortex. All GlyT-1 inhibitors tested, as well as glycine itself, competed fully for the binding of both [ 3H]-SB-733993 and [ 3H]-GSK931145 in both hGlyT-1 and rat cortex membranes. Studies on the effect of varying NaCl concentration showed that [ 3H]-SB-733993 binding was reduced by >90% in the absence of added Na + ions, whilst [ 3H]-GSK931145 binding was unaffected. Glycine produced concentration-dependent decreases in binding affinity of both radioligands without major changes in B max values, suggesting that both [ 3H]-SB-733993 and [ 3H]-GSK931145 bind to sites on GlyT-1 that are orthosteric to the site at which glycine itself binds. Overall, these results show that both [ 3H]-SB-733993 and [ 3H]-GSK931145 are useful radioligands for studies on GlyT-1 in both cell lines and native tissues, with [ 3H]-GSK931145 being the radioligand of choice for further studies on GlyT-1 expression and pharmacology.

Muscarinic cholinoceptor agonists and antagonists are modulators of the activity of α1-adrenoceptors in the membranes of rat cerebral cortex

The effects of activation and inhibition of muscarinic cholinoceptors by carbachol and atropine on the binding of specific nonselective α1-antagonist [3H]prazosine in synaptosomal membranes of rat cerebral cortex have been studied. It has been shown that the ligand-receptor interaction of α1-adrenoceptors corresponds to the model suggesting the presence of a single receptor pool and the binding of two ligand molecules to the receptor. The parameters of [3H]prazosine binding to α1-adrenoceptors were as follows: Kd = 1.56 ± 0.17 nM, Bmax = 30.25 ± 1.78 fmol/mg protein, n = 2. Upon inhibition of muscarinic cholinoceptors by atropine or their activation by carbachol, the radiolabelled ligand is bound to α1-adrenoceptors according to the same model but at n = 1. In the presence of atropine, the sensitivity of α1-adrenoceptors to [3H]prazosine decreases more than twofold (Kd = 3.52 ± 0.36 nM) and the concentration of the active receptors is 36% lower (Bmax = 19.45 ± 1.46 fmol/mg protein). Carbachol does not reduce the affinity of adrenoceptors to the ligand, while the concentration of active receptors decreases like in the case of atropine. It is supposed that α1-adrenoceptors in the membranes of rat cerebral cortex exist as dimers. The modulating effects of atropine and carbachol on the binding of specific antagonist by α1-adrenoceptors are exhibited as changes in the general character of binding (monomerization of α1-adrenoceptors) and as inhibitory effect on the [3H]prazosine binding parameters.

Neurotensin modulates central muscarinic receptors, an effect which does not involve the high-affinity neurotensin receptor (NTS1)

Neurotensin (NT) is a tridecapeptide distributed in central and peripheral nervous systems, which can behave as a neurotransmitter or neuromodulator at central and peripheral levels. Herein we tested the potential effect of this peptide on quinuclidinyl benzilate ([ 3H]-QNB) binding to muscarinic receptor in rat CNS membranes. It was observed that NT decreased up to 50–70% ligand binding at 1 × 10 − 7 M–1 × 10 − 5 M concentration in cerebral cortex, cerebellum and striatum. In the hippocampus, NT exerted a biphasic effect, behaving as a stimulator in the presence of 1 × 10 − 12 M–1 × 10 − 10 M concentration but as an inhibitor at 1 × 10 − 8 M–1 × 10 − 5 M concentration. In order to test the involvement of high-affinity NT receptor (NTS1) in NT inhibitory effect, assays were carried out in the presence of 1 × 10 − 6 M NT and/or SR 48692 (Sanofi-Aventis, U.S., Inc.), a specific antagonist for this receptor, dissolved in dimethylsulfoxide (DMSO) 10% v/v. As controls, membranes incubated with DMSO and/or NT 1 × 10 − 6 M plus DMSO were processed. It was found that NT + DMSO decreased [ 3H]-QNB binding to cerebral cortex, cerebellum and hippocampal membranes by 49%, 32% and 53%, respectively. This inhibition was not observed with the DMSO control group. Membrane preincubation with 1 × 10 − 6 M SR 48692 failed to alter NT effect on binding. SR 48692 at 1 × 10 − 6 M concentration decreased the binding by 50% only in cerebral cortex membranes, suggesting a possible direct effect of the antagonist on muscarinic receptors in this area. It was therefore concluded that the high-affinity NT receptor may not be involved in ligand binding inhibition to muscarinic receptor by NT.

Synthesis and biological activity of the calcium modulator ( R) and ( S)-3-methyl 5-pentyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate

An efficient total synthesis of ( R) and ( S)-3-methyl 5-pentyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate in high optical purities is reported. The useful step is the resolution of racemic 2, 6-dimethyl-5-methoxycarbonyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3-carboxylic acid by using commercially available Cinchona alkaloids cinchonidine and quinidine as the resolving agents. Under the optimum conditions, the optical purities for R- and S-enantiomers are extremely high (ee >99.5%). The further dihydropyridine receptor binding activity assay shows that the S-enantiomer is more potent than R-enantiomer both in rat cardiac (approximately 19 times) and cerebral cortex membrane (12 times).

Allosteric modulation of the [3H]quinuclidinyl benzylate binding to M-cholinoreceptors in rat cerebral cortex by adrenotropic agents

The allosteric effects of adrenotropic drugs and the membranotropic agent cocaine on the kinetics of [3H]quinuclidinyl benzylate ([3H]QNB) binding to muscarine cholinoceptors of synaptosomal membranes of rat cerebral cortex were studied. In control, the best results were obtained for the model that assumes the existence of two receptor pools (with high and low affinity) with calculated parameters of the activity (K d), amount (B max), and mono- to dimer receptors ratio (n). For the high-affinity receptors these parameters were K d1 = 0.18 ± 0.08 nM, B m1 = 221.2 ± 56.7 fmol/mg protein, n 1 = 2, and for low-affinity receptors, K d2 = 1.33 ± 0.11 nM, B m2 = 748.7 ± 53.3 fmol/mg protein, n 2 = 2. Allosteric modulation of the activity of specific neurotransmitter receptors can be accomplished by changing the receptor affinity and amount as well as the proportion of mono- and dimer receptors. Under control conditions, muscarine receptors exist as dimers. In the presence of α-adrenoreceptor agonist noradrenaline and β-adrenoreceptor antagonist propranolol, only one pool of the dimer muscarine receptors remains. The number of binding sites for noradrenaline and propranolol decreases approximately by 40% and 20%, respectively. The agonist of α2-adrenoreceptors clonidine, the antagonist of α2-adrenoreceptors yohimbine, and a membranotropic agent cocaine change the ligand binding so that only one receptor pool remains but some of the dimer receptors become monomeric (1 < n < 2). The amount of binding sites reduces by 20%, 25%, and 45% for clonidine, yohimbine, and cocaine, respectively.

Humanin Structural Versatility and Interaction with Model Cerebral Cortex Membranes

Humanin (HN) is a recently identified neuroprotective peptide able to inhibit neurotoxicity induced by various insults which can be related to Alzheimer disease (AD) as well as to cell death induced by other stimuli. Previous CD and NMR studies demonstrated that HN adopts an unordered conformation in water, a alpha-helix conformation in 30% TFE, and a beta-sheet structure in PBS. Furthermore, other studies clearly indicated HN as a secreted peptide, able to prevent neuronal cell death caused by amyloid beta (Abeta) derivatives. Although Abeta was found to interact with neuronal membranes, currently there is not experimental evidence unveiling HN interaction with membranes. In this paper a spin labeling technique coupled with electron paramagnetic resonance (EPR) and circular dichroism (CD) has been used to study the structure and dynamics of HN in solution and for the first time in the presence of model cerebral cortex membranes (CCM). We have demonstrated that HN has a great tendency to aggregate even at low concentrations in water solutions at different ionic strengths and monomerizes in the TFE apolar environment. We also showed that HN slightly perturbs model CCM at the surface assuming a clear beta-sheet conformation. In addition, HN increases the fluidity of the bilayer core without penetrating into the membrane.

Intracerebroventricular Administration of Ouabain to Rats Changes the Expression of NMDA Receptor Subunits in Cerebral Cortex and Hippocampus

Ouabain exerts neurotoxic action and activates the population of NMDA receptors. Herein the effect of ouabain on the expression of NMDA subunits was evaluated. Adult Wistar rats were administered intracerebroventricularly with 0.1, 10 and 100 nmol ouabain or saline solution (control). Two days later, membranes of cerebral cortex and hippocampus were isolated. Western blots with antibodies for the NMDA receptor subunits: NR1; NR2A; NR2B; NR2C and NR2D were carried out. In cerebral cortex, NR2D subunit increased 30% with 10 nmol ouabain dose. With 100 nmol ouabain, NR1 and NR2D subunits enhanced 40 and 20%, respectively. In hippocampus, with the dose of 0.1 nmol ouabain, NR1 subunit enhanced roughly 50% whereas NR2B subunit decreased 30%. After administration of 10 nmol ouabain dose, NR2A, NR2B and NR2C subunits decreased 40, 50 and 30%, respectively. With the dose of 100 nmol of ouabain, NR1, NR2A and NR2B subunits diminished 10-20%. It is concluded that ouabain administration led to a differential regulation in the expression of NMDA subunits. These results may be correlated with the modulatory action of ouabain on NMDA receptor.

Comparative characteristics of binding kinetics of specific antagonists by α1- and α2-adrenoceptors in rat cerebral cortex membranes

The binding of specific nonselective α1- and α2-adrenoceptor antagonists [3H]prazosine and [3H]RX821002 has been studied on rat cerebral cortex synaptosomal membranes. It is shown that for α1-adrenoceptors the ligand-receptor interaction corresponds to the model assuming the presence of one pool of receptors and binding of two ligand molecules to the receptor. The parameters of [3H]prazosine binding to α1-adrenoceptors were: Kd= 1.56 ± 0.17 nM, Bmax = 30.25 ± 1.78 fmol/mg protein, n = 2. The parameters of [3H]RX821002 binding to α2-adrenoceptors were: Kd = 1.94 ± 0.08 nM, Bmax = 12.77 ± 3.17 fmol/mg protein, n = 2. For α2 -adrenoceptors the ligand-receptor interaction corresponded to the same model. For α1 - and α2-adrenoceptor antagonists the dissociation constants (Kd) are approximately equal (1.56 ± 0.17 and 1.94 ± 0.08 nM, respectively), but the concentration of α2-adrenoceptors is two times lower than that of α1-adrenoceptors ( 12.77 ± 3.17 and 30.25 ± 1.78 fmol/mg protein, respectively). The efficiency (E = Bmax/2Kd) of the ligand binding to α1-adrenoceptors is 2.3 times higher than that to α2-adrenoceptors (7.46 ± 1.32 and 3.29 ± 0.68 fmol/mg protein/nM, respectively. The data suggest that α1- and α2 -adrenoceptors in rat cerebral cortex exist as dimers.

Comparison of the binding affinity of CGP-12177A at recombinant rat α 1D-adrenoceptors expressed in BHK-21 cell membranes and α 1-adrenoceptors present in rat cerebral cortex membranes

Recent in vitro studies, performed in rat aorta, mesenteric and intrapulmonary arteries, and human pulmonary artery, demonstrated that the β-adrenoceptor ligand CGP-12177A (4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one) is also provided with antagonist or partial agonist properties at α 1-adrenoceptors. These observations were supported by estimates of CGP-12177A binding affinity at α 1-adrenoceptors, which have been always performed in rat cerebral cortex membranes, as a surrogate of vascular tissue. Since α 1D-adrenoceptors are predominant in both rat aorta and mesenteric artery, in the present study, we measured, for the first time, the binding affinity of CGP-12177A at recombinant rat α 1D-adrenoceptors expressed in BHK-21 cell membranes. CGP-12177A binding affinity was also determined in rat cerebral cortex membranes, where various α 1-adrenoceptor subtypes are present. By means of [ 3H]prazosin binding competition experiments, we found that CGP-12177A bound to α 1D-adrenoceptor-expressing BHK-21 cell membranes, with a binding affinity (p K i = 5.39 ± 0.27) almost identical to that measured in cerebral membranes (p K i = 5.44 ± 0.07), indicating that it is a non-subtype selective α 1-adrenoceptor ligand. Moreover, CGP-12177A binding affinity was very close to its functional affinity evaluated in rat aorta in terms of antagonist potency against phenylephrine-induced contraction (p K B = 5.65 ± 0.07). In conclusion, our results demonstrate that, in order to evaluate CGP-12177A binding affinity at aorta and mesenteric artery α 1-adrenoceptors, estimates in rat cerebral membranes are as reliable as those in recombinant rat α 1D-adrenoceptors, since both values are very close to CGP-12177A functional affinities in isolated vessels.

Reciprocal inhibition of G-protein signaling is induced by CB 1 cannabinoid and GABA B receptor interactions in rat hippocampal membranes

Cannabinoid CB 1 and the metabotropic GABA B receptors have been shown to display similar pharmacological effects and co-localization in certain brain regions. Previous studies have reported a functional link between the two systems. As a first step to investigate the underlying molecular mechanism, here we show cross-inhibition of G-protein signaling between GABA B and CB 1 receptors in rat hippocampal membranes. The CB 1 agonist R-Win55,212-2 displayed high potency and efficacy in stimulating guanosine-5′- O-(3-[ 35S]thio)triphosphate, [ 35S]GTPγS binding. Its effect was completely blocked by the specific CB 1 antagonist AM251 suggesting that the signaling was via CB 1 receptors. The GABA B agonists baclofen and SKF97541 also elevated [ 35S]GTPγS binding by about 60%, with potency values in the micromolar range. Phaclofen behaved as a low potency antagonist with an ED 50 ≈ 1 mM. However, phaclofen at low doses (1 and 10 nM) slightly but significantly attenuated maximal stimulation of [ 35S]GTPγS binding by the CB 1 agonist R-Win55,212-2. The observation that higher concentrations of phaclofen had no such effect rule out the possibility of its direct action on CB 1 receptors. The pharmacologically inactive stereoisomer S-Win55,212-3 had no effect either alone or in combination with phaclofen establishing that the interaction is stereospecific in hippocampus. The specific CB 1 antagonist AM251 at a low dose (1 nM) also inhibited the efficacy of G-protein signaling of the GABA B receptor agonist SKF97541. Cross-talk of the two receptor systems was not detected in either spinal cord or cerebral cortex membranes. It is speculated that the interaction might occur via an allosteric interaction between a subset of GABA B and CB 1 receptors in rat hippocampal membranes. Although the exact molecular mechanism of the reciprocal inhibition between CB 1 and GABA B receptors will have to be explored by future studies it is intriguing that the cross-talk might be involved in balance tuning the endocannabinoid and GABAergic signaling in hippocampus.

Different affinities of native α1B-adrenoceptors for ketanserin between intact tissue segments and membrane preparations

The pharmacological profiles of α1-adrenoceptors for ketanserin, prazosin, silodosin, and BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]decane-7,9-dione dihydrochloride) were examined under different assay conditions. Among the tested antagonists and α1-adrenoceptors subtypes, ketanserin showed significantly lower affinity for the α1B-adrenoceptor subtype in intact tissue sampled from the rat tail artery, thoracic aorta, and cerebral cortex (functional pKB and binding pKi were approximately 6), than in cerebral cortex membrane preparations or whole cell and membrane preparations of α1B-adrenoceptor transfected Human Embryonic Kidney 293T (HEK 293T) cells (pKi was approximately 8). In these tissues and cells, however, ketanserin showed a similar affinity (pKi = approximately 8) for α1A- and α1D-adrenoceptors even though the assays were conducted under different conditions. In contrast, the affinities of α1A-, α1B-, and α1D-adrenoceptors for prazosin, silodosin, and BMY 7378 did not significantly change under different assay conditions and in different tissues. The present study reveals that the pharmacological profiles of native α 1B-adrenoceptors for ketanserin is strongly influenced by the assay conditions and suggest that antagonist affinity is not necessarily constant.